1. Field of the Invention
The present invention relates to a magnetoresistive random access memory.
2. Description of the Related Art
The magnetoresistive random access memory (MRAM) is a device that stores information by using the magnetoresistive effect. The MRAM has volatility, a high operating speed, a high integration degree, and high reliability, and hence is expected as a nonvolatile random access memory capable of replacing a DRAM, EEPROM, and the like. In particular, a spin-transfer-torque-write MRAM using magnetization reversal caused by spin current transfer has been attracting attention in recent years because the device has high scalability to micropatterning.
In the spin-transfer-torque-write MRAM, write and read operations are equal in that a current is supplied to a memory cell, and the only difference is the magnitude of the memory cell current. When the read current is large, therefore, the possibility of occurrence of a write error (read disturbance) in a memory cell increases.
To avoid this read disturbance, the read current need only be decreased, and many read methods that achieve this effect have been conventionally proposed. However, decreasing the read current is equivalent to decreasing the resistance against variations in a circuit and decreasing the read speed. This makes it difficult for the spin-transfer-torque-write MRAM to replace a DRAM required to have a large capacity and high speed. Accordingly, demands have arisen for increasing the read current by using a read method capable of avoiding the read disturbance.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-241013 has proposed a method of supplying a current for canceling out a magnetic field generated by a current supplied when writing data to a selected memory cell, in order to prevent the magnetic field from exerting influence on an unselected adjacent memory cell. However, this method has no special improvement on a read operation.
In the prior art as explained above, the read current must be decreased because read disturbance may occur if the read current increases. This makes it impossible to provide a high-speed MRAM.